Generally, various fibers such as acrylic base fiber, polyvinyl chloride base fiber, and polyester fiber have been available commercially as artificial hair fibers. However, there were no fiber that could satisfy all characteristics needed as artificial hair fiber such as heat resistance, curling characteristics, touch feeling, and thus, a hair decorative product satisfying the various characteristic could not be obtained only by these fibers in production of a hair decorative product, and products having a characteristic of the fibers each are used in practice.
For example, acrylic base fiber has advantages that it is similar in volume, touch feeling, and brilliance to natural hair and superior in combing smoothness, but also has problems in curling characteristic such as twist of hair bundle by curling, loosening of curled hair over time, and deficiency of elasticity, and thus, has been used mainly for naturally waved hair (no or softly waved hair). In contrast, vinyl chloride fiber has the advantage that it is superior in curling-related characteristics such as tightness of curled hair, resistance to loosening over time, and elasticity when curled spirally, but also has disadvantages such as poor volume and poor sensory characteristics giving touch feeling and brilliance similar to synthetic fiber, and, thus, has been widely used for waved or terminal-curled straight hair.
Thus, for example, various studies on composition of a fiber were made for production of a fiber having the characteristics of both conventional acrylic base fiber and polyvinyl chloride base fiber; and Japanese Unexamined Patent Publication No. 2-53910 proposed a hair fiber superior in cosmetic characteristics that is made of a copolymer containing 15 to 30 wt % of acrylonitrile and 85 to 70 wt % of vinyl chloride, has a H- to dumbbell-shaped cross-sectional shape, and a monofilament fineness of 44 to 78 decitexes; but it has problems that the composition above is likely to produce the copolymer in low heat resistance and a circularity coefficient becomes 1.8 or less due to the H- to dumbbell-shaped cross-sectional shape, and thus soft touch feeling is not obtained due to the rigidity of curled hair. Alternatively, for improvement by mixing of acrylic base fiber and polyvinyl chloride base fiber, Japanese Unexamined Patent Publication 2002-227020 proposed an artificial hair fiber bundle consisting of 20 to 80 wt parts of acrylic base fiber having a monofilament fineness of 30 to 85 decitexes and 20 to 80 wt parts of a vinyl chloride base fiber having a monofilament fineness of 30 to 85 decitexes that can be adopted in a variety range of hair styles without deterioration in the characteristics of both fibers. However, the hair fiber bundle of above composition has various disadvantages in quality since the fiber bundle has simple composition formed of mixture of two kinds of fibers. For example, the hair fiber bundle was insufficient in stylability such as volume and straightness and also in sensory characteristics such as brilliance, combing smoothness and touch feeling, and thus, products modest in quality were only produced.